#include <bits/stdc++.h>
using namespace std;


char s[1000], ans[1000];

namespace judger {
    char s[3000], buf[300];
    int cnt;
    int n;
    void init(int _n)
    {
        n = _n;
        for (int i=0; i<n; ++i)
            s[i] = rand()%2 + 'a';
        printf("spell: %s\n", s);
    }


}

inline void submit(char s[])
{
    printf("%s\n", s); fflush(stdout);
    // #endif
}

inline int ask()
{
    int x; scanf("%d", &x);
    if (x == 0) exit(0);
    return x;
}


int main(int argc, char const *argv[])
{
    memset(s, 'a', 300);
    s[300] = 0;
    submit(s);
    int la = 300-ask();
    memset(s, 'a', la);
    s[la] = 0;
    if (la == 0)
    {
        memset(s, 'b', 300); submit(s);
        int lb = 300 - ask();
        s[lb] = 0;
        submit(s);
        int x = ask();
        assert(x == 0);
        return 0;
    }
    submit(s);
    int lb = ask(), len = la + lb;
    memset(s, 'a', la + lb);
    s[len] = 0;
    strcpy(ans, s);
    int base = lb;
    for (int i=0; i<len-1; ++i)
    {
        s[i] = 'b';
        submit(s);
        int tans = ask();
        if (tans < base) {
            base = tans;
        } else
            s[i] = 'a';
    }
    if (base > 0) s[len-1] = 'b';
    printf("%s\n", s);
    return 0;
}
